Old Concrete Beam Schedule - Interpretation

[RFreund]

Please see the attached concrete beam schedule.

How is the reinforcement placed in the T9 Beam?
Should these bars be bent or is my section correct.
I forgot to show the stirrups but I understand the placement of those.

Thanks!



EIT

 

[RFreund]

Also these plans would be from approx 1920's - 1930's I believe.

EIT

 

[BAretired]

I doubt that your interpretation is correct, but the schedule is not completely clear to me either. I suspect that what you have is 2 - 1" square bars bottom and 2 - 1¹/₈" square bars bent according to Profile T9 which should be detailed somewhere on the drawings.

There are probably a couple of top bars used to tie the stirrups, but they would likely be nominal, perhaps 2-1/2" square bars.

You probably should X-ray the beam to be sure.

BA

 

[mtu1972]

I think BA is right. So you should have 4 bars in the bottom and 4 bars at the top where the beam is continuous over a column.

My oldest cocnrete standard is the 1940 Portland Cement Association's Standard Specification for Concrete and Reinforced Concrete and it lists the allowable strengths for reinforcing as 18,000 psi for structural grade steel bars and 20,000 psi for intermediate grade steel bars.

Since your building is older than that, you should be conservative on what strength is assumed.

gjc

 

[RFreund]

Thanks,

I didn't think my interpretation was correct either, I was assuming they must be bent but was not sure. I will look for the profile T9.
Also I will see what those steel grades yield for a result.


Thanks.

EIT

 

[dcarr82775]

Bar type T9 coudl refer to a 'truss' bar which is bent such that it is high over the columns and low at mid-span. I have come across that type of bar a lot in older CIP buildings.

My interpretation is:

2-1" sq bars bottom
2-1.125" sq bars bottom midspan
2-1.125" sq bars top over supports

 

[hokie66]

I agree there are probably 4 bars in the bottom and 2 of them go into the top layer, but you would have to check the adjacent spans to know how many top bars extend into this span.

 

[BAretired]

I remember when I started engineering in Toronto, Ontario in the 1950's looking over some old drawings dating from the 1920's. There were continuous concrete beams reinforced entirely with bottom steel...no bent bars and no top bars. Who worried about a little cracking over the supports? Strangely enough, the beams were performing quite well after thirty years of service.

BA

 

[RFreund]

Thanks guys,

I'll check both 1.) 2 top continuous and 2.) Simple span 4 bars in bottom and see what kind of allowable live load I end up with.

I'm just trying to get a approximate allowable live load.



EIT

 

[JLNJ]

The truss bars from adjacent spans probably lap at the column so you in effect will have 4 top bars at the column. There may be few enough stirrups that there are none at mid-span and therefore no additional continuous top bars are present.

Somewhere on the drawings it probably addresses the bar strength - higher strength bars might be referred to as "hard" grade.

 

[larsacious]

I suspect you are dealing with all square bar reinforcing. You have 4 bars at mid-span (2 straight bars and 2 truss bars). The truss bars will bend up somewhere near the point of inflection and become top bars at the support and will lap with top bars from the adjacent spans. There are a total of 26 stirrups in your beam. They are 13 of them spaced as indicated in the schedule from each end.

I analyzed a structure similar to this about 4 years ago. Here are some of the challenges I faced:
-My section was under-reinforced in shear. At first glance you seem to have lucked out and there is plenty of shear reinforcing.
-Development length can be an issue as you have to check bond.

 

[BAretired]

The square bars were normally twisted, but they were plain stock with much lower bond strength than deformed bars.

BA

 

[RFreund]

Forgot I wanted to follow up with this.

After running the numbers and seeing what kind of allowable live loads I ended up with it seems that there should be (4) bars at the top of the section over supports as you pointed out. Thanks for the info because at first with only 2 bars at the top things were not working out so well.

EIT